The Critical Role of Notch1–TLR 4 Signaling in the Inflammatory and Fungicidal Activity of Macrophages Against Paracoccidioides brasiliensis Strain Pb18

The immunosuppressive activity of myeloid-derived suppressor cells in murine Paracoccidioidomycosis relies on Indoleamine 2,3-dioxygenase activity and Dectin-1 and TLRs signaling

Paracoccidioidomycosis (PCM) is a systemic mycosis with a high incidence in Latin America. Prior studies have demonstrated the significance of the enzyme Indoleamine 2,3-dioxygenase (IDO-1) in the immune regulation of PCM as well as the vital role of myeloid-derived suppressor cells (MDSCs) in moderating PCM severity. Additionally, Dectin-1 and Toll-Like Receptors (TLRs) signaling in cancer, infection, and autoimmune diseases have been shown to impact MDSC-IDO-1⁺ activity. To expand our understanding of MDSCs and the role of IDO-1 and pattern recognition receptors (PRRs) signaling in PCM, we generated MDSCs in vitro and administered an IDO-1 inhibitor before challenging the cells with Paracoccidioides brasiliensis yeasts. By co-culturing MDSCs with lymphocytes, we assessed T-cell proliferation to examine the influence of IDO-1 on MDSC activity. Moreover, we utilized specific antibodies and MDSCs from Dectin-1, TLR4, and TLR2 knockout mice to evaluate the effect of these PRRs on IDO-1 production by MDSCs. We confirmed the importance of these in vitro findings by assessing MDSC-IDO-1⁺ in the lungs of mice following the fungal infection. Taken together, our data show that IDO-1 expression by MDSCs is crucial for the control of T-cell proliferation, and the production of this enzyme is partially dependent on Dectin-1, TLR2, and TLR4 signaling during murine PCM.

The Role of Dimorphism Regulating Histidine Kinase (Drk1) in the Pathogenic Fungus Paracoccidioides brasiliensis Cell Wall

Dimorphic fungi of the Paracoccidioides genus are the causative agents of paracoccidioidomycosis (PCM), an endemic disease in Latin America with a high incidence in Brazil. This pathogen presents as infective mycelium at 25 °C in the soil, reverting to its pathogenic form when inhaled by the mammalian host (37 °C). Among these dimorphic fungal species, dimorphism regulating histidine kinase (Drk1) plays an essential role in the morphological transition. These kinases are present in bacteria and fungi but absent in mammalian cells and are important virulence and cellular survival regulators. Hence, the purpose of this study was to investigate the role of PbDrk1 in the cell wall modulation of P. brasiliensis. We observed that PbDrk1 participates in fungal resistance to different cell wall-disturbing agents by reducing viability after treatment with iDrk1. To verify the role of PbDRK1 in cell wall morphogenesis, qPCR results showed that samples previously exposed to iDrk1 presented higher expression levels of several genes related to cell wall modulation. One of them was FKS1, a β-glucan synthase that showed a 3.6-fold increase. Furthermore, confocal microscopy analysis and flow cytometry showed higher β-glucan exposure on the cell surface of P. brasiliensis after incubation with iDrk1. Accordingly, through phagocytosis assays, a significantly higher phagocytic index was observed in yeasts treated with iDrk1 than the control group, demonstrating the role of PbDrk1 in cell wall modulation, which then becomes a relevant target to be investigated. In parallel, the immune response profile showed increased levels of proinflammatory cytokines. Finally, our data strongly suggest that PbDrk1 modulates cell wall component expression, among which we can identify β-glucan. Understanding this signalling pathway may be of great value for identifying targets of antifungal molecular activity since HKs are not present in mammals.

Long non-coding RNA CHRF accelerates LPS-induced acute lung injury through microRNA-146a/Notch1 axis

Background

The present study sought to investigate the regulatory role of the long non-coding RNA (lncRNA) cardiac hypertrophy-related factor (CHRF) in a mouse model of acute lung injury (ALI) and in primary mouse pulmonary microvascular endothelial cells (MPVECs) treated with lipopolysaccharide (LPS).

Methods

C57BL/6 mice were given adenovirus (Ad) sh-CHRF or negative control (NC) before undergoing cecal ligation and perforation. MPVECs transfected with Adsh-CHRF or NC were treated with LPS. Double luciferase assay was used to detect the binding of miR-146a to CHRF or Notch1. Subsequently, MPVECs were co-transfected with miR-146a inhibitor and sh-CHRF for 24 hours, and then treated with LPS.

Results

High expression of CHRF was detected in septic mice. Cecal ligation and perforation induced ALI and apoptosis in mice, whereas, CHRF knockout could inhibit ALI. The protein expression levels of TNF-α, IL-1β and IL-6 in the lung and bronchoalveolar lavage fluid of the CLP group were up-regulated, whereas the expression of IL-4 and IL-10 was down-regulated. CHRF inhibition reduced the production of proinflammatory cytokines in septic mice. The inhibitory effect of CHRF gene knockdown on lung inflammation and apoptosis was confirmed in the septic cell model. Mechanistic investigation showed that CHRF up-regulated the level of Notch1 by sponging miR-146a. Additionally, the low expression of miR-146a reversed the inhibitory effect of CHRF gene knockout on LPS-induced inflammatory response and apoptosis. Together, in vivo and in vitro results demonstrated that CHRF enhanced sepsis-induced ALI by targeting miR-146a and up-regulating Notch1.

Conclusions

CHRF can induce inflammation and apoptosis caused by sepsis by miR-146a/Notch1 axis. Therefore, it may serve as a potential drug target for treating sepsis-induced ALI.

Notch Signaling Ligand Jagged1 Enhances Macrophage-Mediated Response to Helicobacter pylori

Helicobacter pylori (H. pylori) is one of the gram-negative bacteria that mainly colonize the stomach mucosa and cause many gastrointestinal diseases, such as gastritis, peptic ulcer, and gastric cancer. Macrophages play a key role in eradicating H. pylori. Recent data have shown that Notch signaling could modulate the activation and bactericidal activities of macrophages. However, the role of Notch signaling in macrophages against H. pylori remains unclear. In the present study, in the co-culture model of macrophages with H. pylori, the inhibition of Notch signaling using γ-secretase decreased the expression of inducible nitric oxide synthase (iNOS) and its product, nitric oxide (NO), and downregulated the secretion of pro-inflammatory cytokine and attenuated phagocytosis and bactericidal activities of macrophages to H. pylori. Furthermore, we identified that Jagged1, one of Notch signaling ligands, was both upregulated in mRNA and protein level in activated macrophages induced by H. pylori. Clinical specimens showed that the number of Jagged1⁺ macrophages in the stomach mucosa from H. pylori-infected patients was significantly higher than that in healthy control. The overexpression of Jagged1 promoted bactericidal activities of macrophages against H. pylori and siRNA-Jagged1 presented the opposite effect. Besides, the addition of exogenous rJagged1 facilitated the pro-inflammatory mediators of macrophages against H. pylori, but the treatment of anti-Jagged1 neutralizing antibody attenuated it. Taken together, these results suggest that Jagged1 is a promoting molecule for macrophages against H. pylori, which will provide insight for exploring Jagged1 as a novel therapeutic target for the control of H. pylori infection.

Notch signaling pathway in infectious diseases: role in the regulation of immune response

BACKGROUND

The Notch signaling pathway is a cell signaling system that is conserved in a variety of eukaryotes. Overall, Notch receptors and their ligands are single-pass transmembrane proteins, which often require cell-cell interactions and proteolytic processing to promote signaling. Since its discovery, it has been the subject of extensive research that revealed its importance in several cellular mechanisms, including cell fate determination, hematopoiesis, tissue self-renewal, proliferation, and apoptosis during embryogenesis. Many studies have described the influence of the Notch pathway in modulating the innate and adaptive immune systems.

METHODS

We analyzed the literature on the role of the Notch pathway in regulating immune responses during infections, aiming to discuss the importance of establishing a Notch signaling pathway-based approach for predicting the outcome of infectious diseases.

CONCLUSION

In this review, we present an overview of evidence that demonstrates the direct and indirect effects of interaction between the Notch signaling pathway and the immune responses against bacterial, viral, fungal, and parasitic infections, as well as the importance of this pathway to predict the outcome of infectious diseases.

TLR3 Is a Negative Regulator of Immune Responses Against Paracoccidioides brasiliensis

Toll-like receptors (TLRs) comprise the best-characterized pattern-recognition receptor (PRR) family able to activate distinct immune responses depending on the receptor/adaptor set assembled. TLRs, such as TLR2, TLR4 and TLR9, and their signaling were shown to be important in Paracoccidioides brasiliensis infections. However, the role of the endosomal TLR3 in experimental paracoccidioidomycosys remains obscure. In vitro assays, macrophages of the bone marrow of WT or TLR3^−/− mice were differentiated for evaluation of their microbicidal activity. In vivo assays, WT or TLR3^−/− mice were infected intratracheally with Paracoccidioides brasiliensis yeasts for investigation of the lung response type induced. The cytotoxic activity of CD8⁺ T cells was assessed by cytotoxicity assay. To confirm the importance of CD8⁺ T cells in the control of infection in the absence of tlr3, a depletion assay of these cells was performed. Here, we show for the first time that TLR3 modulate the infection against Paracoccidioides brasiliensis by dampening pro-inflammatory response, NO production, IFN⁺CD8⁺T, and IL-17⁺CD8⁺T cell activation and cytotoxic function, associated with granzyme B and perforin down regulation. As conclusion, we suggest that TLR3 could be used as an escape mechanism of the fungus in an experimental paracoccidioidomycosis.

Crosstalk between Toll-like receptor 3 and Notch signaling contributes to CD14+ monocytes activity in enterovirus 71 infected hand, foot, and mouth disease

Interaction between Toll-like receptor (TLR) and Notch signaling contributes to inflammatory response in nephropathy and fungicidal infection, however, the role of this crosstalk remains not fully elucidated in enterovirus 71 (EV71)-induced hand, foot, and mouth disease (HFMD). The aim of this study was to investigate the crosstalk between TLR and Notch in inflammatory regulation in EV71 infection. Thirty-seven EV-71-indcued HFMD (16 mild and 21 severe cases) and eleven normal control (NC) were enrolled. CD14⁺ monocytes were purified, and were stimulated with either TLR3/4 agonists [poly(I: C) or LPS] or Notch signaling inhibitor. TLRs and Notch receptors expression, proinflammatory cytokines production, and important molecules in signaling pathways were measured by real-time PCR, ELISA, and Western blot. TLR3 and TLR4 was significantly elevated in CD14⁺ monocytes from HFMD patients than NC. Notch1 and Notch2 mRNA was also remarkably increased in CD14⁺ monocytes from severe HFMD. Poly(I: C) stimulation resulted in robust increase of IL-8, IL-6, and TNF-α by CD14⁺ monocytes in severe HFMD compared to NC. Activation of Notch1, Notch2, and target genes, Hes1 and Hes5 was also enhanced upon ploy(I: C) treatment. Although inhibition of Notch signaling did not affect TLR3 expression, poly(I: C)-induced inflammatory response was robustly attenuated, which was accompanied by silencing Src phosphorylation in CD14⁺ monocytes from severe HFMD patients. The current data indicated that crosstalk between TLR3 and Notch signaling modulated CD14⁺ monocytes function and inflammatory responses in the progression of EV71-induced HFMD.